chemistry question help?

Question

the equation for the synthesis of ammonia is N2 + 3 H2 ---> 2NH3. how many grams of H2 are needed to produce 45 mol NH3 ?

Can someone explain this and how to do it step by step...

Answer 1

From the balanced equation, you need 3 moles of hydrogen to produce 2 moles of ammonia. This also means 30 moles of H2 to give 20 moles of NH3. 60 moles H2 gives 40 moles NH3.

Using this method you can easily estimate that to get 45 moles NH3 you need more than 60 moles of H2. This method helps you analyze if your calculations are in the ballpark.

The calculation is moles H2 = 45 molesNH3 x (3 H2)/(2 NH3)

= 67.5 moles (which is good)

Now to get the grams , multilply moles by molar mass of H2 =2

or g Hydrogen = 67.5 moles x (2 g)/mole hydrogen
= 135 g

Answer 2

1) from the balanced equation 3 H2 --> 2 NH3. 3:2 ratio
so 3/2 x 45 moles = 67.5 moles H2

maybe easier to see like this....

45 moles NH3 x (3 moles H2 / 2 moles NH3) = 67.5 moles H2

2) convert moles to grams..

moles = mass / molecular weight
mass = moles x molecular weight
molecular weight H2 = 1 x 2 = 2 grams / mole (from periodic table)
so mass = 67.5 moles H2 x (2 grams H2/ mole H2) = 135 grams